Process for the production of boron carbide



Unite States Patt ifiiiiiii ing the temperature of reaction and usingdiiferent size magnesium powders it is possible to control the particle 2 834 651 size of the powder produced. Thismeans of control of. particle size. is particularly valuable for the preparation PROCESS FOR THE PROgJIIIECTION F BORON 5 of abrasive polishing powders, in which grain size has. to

be keptwithin very small limits, and also in the prepara- 0 tion of powders-for subsequent sintering and hot-pressing Edam. Garry Gray Longford England operations, where uniformity and control of grain size is .No Drawing. Application May 21, 1953 an important factor in the quality of the sintered material.

Serial No. 356,599 T he heating can be carried out in any desired furnace,

9 Claims. (CL 23 z08) l provided that the whole of the charge is brought up to the desired temperature. Preferably the reaction takes place in a non-oxidising'atmosphere, i. e. an inert or reducing atmosphere, which is maintained also throughout. This invention relates to the'production of boron carthe cooling stage, This ensures a high yield of boron bide powders. carbide. The heating is preferably carried out in a tube Various methods may be employed for the production furnace, such as a carbon tube furnace, where the charge of boron carbide powders. Generally these methods neis entered from one-end and moves continuously through 1 cessitate the employment of very high temperatures and the furnace to the other end. Boats or charging tubes yield'apmelted product which has to be subsequently subwhichwill withstand the temperature are'used as con-v mittedto laborious crushing and grading operations. For tainers for the charge andthe furnace is provided with example, one known method consists in reacting pure a constant flow of burnt town gas, nitrogen or hydrogen; boric anhydride and petroleum coke at a temperature of The leaching treatment, which may be carried out with about 2400 C., which is substantially the melting point hot dilute hydrochloric. sulphuric or nitric acid, removes. of boron Carbide, With the formation around the CaIbOH metals, oxides -and salts present in the boron carbide.

resistor of the furnace of an ingot of boron C r e, After leaching, the product is filtered, washed and dried,. which has to be separated from the rest of the unreacted for xample by the use of a,.fi1ter press.

m crushed and gr T p u in is. g n- The starting materialsconsisting of the boron containerally contaminated with uncombined carbon, whose aba; ing at ial d. the e rbon, b th i a finely divided sorption by the melted carbide at these temperatures is state, maybe mixed intimately and magnesium or mag almost unavoidable. nesium alloys (in the form of thin turnings or powder) .According to the present invention there is provided a ubsequently. dd d, I I Process for the Production of boron carbide P The proportion of each material in .the charge should i the Steps of heating a Charge Containing Carbon, be arranged so that the amount of boron containing ma- Calcined boric acid (boric Oxide, 2 3) a h terial is in excess to "the amount theoretically required, n nesium or magn s m at temperature b andthe-composition of the final product is governed and IOW'thB melting Point Of boron carbide t P Qt controlled by the ratio carbon/magnesium in the charge. mation of boron carbide and subsequently separating the Wh n th tio magnesium/carbon is in the vicinity Produced boron Carbide y a leaching treatment of 15 to 1, boron carbide is produced corresponding to The boron carbide Powders Produced y the Process of 40 the formula B 0, but boron carbides of higher boron conthe invention are substantially homogeneous and the partent may b b i d b increasing h ratio iticle size of the powders is determined by the temperature urn/carbon in the required proportion. of reaction, increasing temperatures leading to increased One example of the process of the invention is given particle sizes. below.

The measured temperature of reaction which is prefer- 5 Examp 1e ably below 2000 C., is that of the outside of the containers in which the charge is placed, and is measured A charge consisting of parts by weight of anhydrous with, for example, an optical pyrometer. borax (Na B O 20 parts by weight magnesium powder,

The preferred salts of boric acid are alkali-metal tetraand 1.2 parts by weight carbon, is placed in boats or borates, such as dehydrated borax (anhydrous sodium 50 charging tubes. These boats or tubes are continuously tetra-borate, Na B O or alkaline earth metal tetrapassed through a carbon tube furnace at a temperature borates, but meta-borates may also be used. of -16501700 C. The atmosphere in the furnace is The reaction is carrried out at a temperature well bemaintained in a non-oxidising state bypassing nitrogen low the melting point of boron carbide. For example, or hydrogen through the furnace. After cooling, the the charge may be heated to substantially 930 C., at 5 product is leached with hot dilute hydrochloric and nitric which temperature the reaction starts and evolves sufiiacid, to produce approximately 6 parts by weight of boron cient heat to bring the charge to a temperature of 1200- carbide powder containing 77.5% boron and 21.3% car- 1300 C. Further heating may then be necessary to bon. maintain this temperature or increase it, if desired. I claim:

The temperature of the reaction is affected to some ex- 1. A process for the production of boron carbide powtent by the fineness of the reducing agent (magnesium or ders of desired particle size, including the steps of heatmagnesium alloy) employed, since the heat evolved in a ing to a temperature within the range of 930 C. to 2000" given time when reacting increases with increasing fine- C. a charge containing carbon, a material selected from ness. the group consisting of boric oxide (B 0 alkali metal For example, when manufacturing powders of particle tetraborate, and alkali earth metal tetraborate; and a resize all below 2 microns, the temperature has to be kept ducing agent consisting essentially of metallic magnesium,

below 1450 C. preferably using coarse magnesium 1 and subsequently separating the boron carbide by a leachpowder retained on 100 mesh sieve (B. S. 8.). At teming treatment. peratures between 1600-1700" C., the particle size ranges 2. A process for the production of boron carbide powbetween 0 and 5 microns. At temperatures of 1850 C. ders, including the steps of heating to a temperature within and above and usingfine magnesium powder, the average the range of 930 C. to 2000 C., an intimate mixture of particle size ranges from 7 to 20 microns. Thus by varyfinely divided carbon, with a finely divided material selected from the group consisting of boric oxide (B 0 alkali metal tetraborate, and alkali earth metal tetraborate, and a reducing agent consisting essentially of metallic magnesium, and subsequently separating the boron carbide by a leaching treatment.

3. A process for the production of boron carbide powders ofdesired particle size, including the steps of heating to a temperature within the range of 930 C. to 2000" C. in a tube furnace in a non-oxidising atmosphere a charge containing carbon, a material selected from the group consisting of boric oxide (B 03), alkali metal tetraborate, and alkali earth metal tetraborate; and a reducing agent consisting essentially of metallic magnesium, and subsequently separating the boron carbide by a leaching treatment.

4. A process for the production of boron carbide powders, including the steps of heating to a temperature within the range of 930 C. to 2000 C. a charge containing carbon, a material selected from the group consisting of boric oxide (B 0 alkali metal tetraborate, and alkali earth metal tetraborate, and a reducing agent consisting essentially of metallic magnesium, and subsequently separating the boron carbide by a leaching treatment, carried out with a hot dilute acid selected from the group consisting of hydrochloric acid, sulphuric acid and nitric acid.

5. A process for the production of boron carbide powders of desired particle size, including the steps of heating to a temperature within the range of 930 C. to 2000 C. a charge containing carbon, boric oxide (B 0 and metallic magnesium and subsequently separating the produced boron carbide by leaching the oxidised compounds thereof out of the produced boron carbide.

6. A process for the production of boron carbide powders of desired particle size, including the steps of heating to a temperature within the range of 930 C. to 2000 C. a charge containing carbon, an anhydrous alkaline metal tetraborate and metallic magnesium, and subsequently separating the produced boron carbide by leaching the oxidised compounds thereof out of the produced boron carbide.

7. A process for the production of boron carbide powders of desired particle size, including thte steps of heating to a temperature within the range of 930 C. to 2000 C. a charge containing carbon, anhydrous sodiurnborate (Na B O and metallic magnesium, and subsequently separating the produced boron carbide by leaching the oxidised compounds thereof out of the produced boron carbide.

8. A process for the formation of boron carbide powder consisting in charging a vessel with 50 parts by weight of anhydrous sodium borate (Na B o 20 parts by weight of magnesium powder and 1.2 parts by weight of carbon; continuously passing said charged vessel through a carbon tube furnace at a temperature between 1650" C. and 1700" C., simultaneously passing a non-oxidising gas through said furnace; allowing the resulting product to cool and, thereafter, leaching said product with hot dilute hydrochloric and nitric acids.

9. A process. for the production of boron carbide powders of desired particle size, including the steps of heating to a temperature within the range of 930 C. to 2000 C. a charge containing carbon, an anhydrous alkaline earth metal tetraborate and metallic magnesium, and subsequently separating the produced boron carbide by leaching the oxidised compounds thereof out of the produced boron carbide.

References Cited in the file of this patent UNITED STATES PATENTS 966,399 Higgins Aug. 2, 1910 1,473,510 Parsons Nov. 6, 1923 2,155,682 Ridgway Apr. 25, 1939 FOREIGN PATENTS 408,354 Germany Jan. 16, 1925 OTHER REFERENCES Babor et al.: General College Chemistry, 2nd edition, 1940, pages 536-537.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, 1924, vol. 5, page 137. 

1. A PROCESS FOR THE PRODUCTION OF BORON CARBIDE POWDERS OF DESIRED PARTICLE SIZE, INCLUDING THE STEPS OF HEATING TO A TEMPERATURE WITHIN THE RANGE OF 930*C. TO 2000* C. A CHARGE CONTAINING CARBON, A MATERIAL SELECTED FROM THE GROUP CONSISTING OF BORIC OXIDE (B2O3), ALKALI METAL TETRABORATE, AND ALKALI EARTH METAL TETRABORATE; AND A REDUCING AGENT CONSISTING ESSENTIALLY OF METALLIC MAGNESIUM, AND SUBSEQUENTLY SEPARATING THE BORON CARBIDE BY A LEACHING TREATMENT. 